The present invention relates to a method and apparatus for determining and monitoring the opacity of atmospheric pollutants, e.g. a smoke plume at the chimney of the power generating plant, from a remote location and, more particularly, to such a system which is essentially passive, one which does not require the generation and application of radiant energy to the plume as part of the measuring process.
For the most part, the determination of smoke density, e.g. for compliance with environmental legislation requirements, has been mostly subjective. In other words, human observers have been trained to characterize observed smoke plumes based on a prior learning experience. So-called smoke schools are conducted on a regular basis to allow the observers to re-correlate their impressions with actual measurements taken under controlled circumstances. No matter how proficient such observers may become, however, it is readily apparent that the reported observations may be affected by a great many variables beside the actual opacity of the smoke being observed. Not only does the subjective process depend upon the recollection of the observer but the process may also be affected by the state of illumination of the smoke plume and the character of the background against which the plume is observed.
While instruments are available which may be attached to a smoke stack and which will accurately measure smoke opacity, such instruments are not universally employed or available and, further, are subject to failure due to the hostile environment in which they typically operate.
Some attempts have been made to permit remote measurement of smoke plume opacity but these systems have typically employed either the sun as an in-line light source or some other external light source, such as a laser. These requirements for an external light source have typically caused the systems to be difficult to operate and, in some cases, highly unreliable or even dangerous. Further, in many of these systems it was still necessary for a human observer to subjectively make a final measurement or comparison.
Among the several objects of the present invention may be noted that provision of a method and apparatus for measuring the opacity of atmospheric pollutants, such as those contained in a smoke plume; the provision of such a method and system which may be employed remotely from the smoke source; the provision of such a system which is essentially passive, i.e. which does not require the system to apply radiant energy to the plume; the provision of such a method and system which are simple and reliable in operation; and the provision of such a system which is relatively simple and inexpensive. Other objects and features will be in part apparent and in part pointed out hereinafter.